The invention relates to a tubular reactor for catalytic gas phase reactions.
Usually, such reactors exhibit a reactor jacket containing a heat carrier that circulates around a contact tube bundle, which extends between a tube plate at the gas inlet side and a tube plate at the gas outlet side, as well as gas inlet and gas outlet hoods spanning the face sides of the two tube plates. The process gas, usually a gas mixture, that is to be brought to reaction enters a contact tube that contains a catalytic mass via the gas inlet hood and after passing said contact tube exits the reactor via the gas outlet hood. The gas inlet may be located either on the top or bottom side, and as a whole the heat carrier may pass through the reactor in parallel flow or counter flow with regard to the process gas flow. The reactor can also have a multi-step design as shown, for example, in the German Patent No. DE 22 01 528 C, FIG. 5.
Usually, the process gas stream is comprised of two or more material streams that are combined shortly before entering the reactor, that is, its gas inlet hood. In this course, secondary reactions that are harmful to the process or even ignition and deflagration may occur, especially in the immediate area surrounding the generally relatively hot tube plate. Examples of such reaction processes are the production of maleic acid anhydride, phthalic acid anhydride, acrolein and acrylic acid.
Fillers of ceramic materials or a wire mat mesh have been introduced into the gas inlet hood in an effort to prevent such secondary reactions. Other attempts involved insulating the tube endings by using cylinders, because the highest temperatures occur generally at the tube plate on the gas inlet side in the area of the tube ending. However, in the end, none of these measures proved effective or at least dependable for preventing the above mentioned secondary reactions.
The U.S. Pat. No. 2,986,454 A discloses the use of so-called isolation tubes in series prior to the contact tube ends on the reaction gas inlet side, where said isolation tubes are surrounded by a cooling chamber with circulating air. With this arrangement, the entering reaction gas mixture is kept away from hot parts prior to the start of the intended reaction. Although the isolation tubes are connected in series to the following contact tubes in a sealed manner, the air that passes through the cooling chamber is subsequently added to the process gas. It is understood that such a process is limited to certain applications. In addition, the isolation tubes which extend in a pivotal manner into the contact tubes for the purpose of compensating for differing heat expansions form undesirable contractions for adding and removing the catalyst. This applies in particular to reactors with numerous contact tubes, for example, more than 10,000, and a large diameter, for example, 7000 mm, where temperature-related offsets of about 10 mm in the edge zone can be expected.
Furthermore, it is known from the U.K. Patent No. 776 416 A to provide a poured and thereafter hardened heat insulation layer at the tube plates on the side of the heat carrier to avoid crystallization in a tubular heat exchanger for cooling or heating of saturated solutions, where said heat exchanger also exhibits a heat carrier that circulates around a tube bundle that stretches between two tube plates. However, such materials, such as artificial resin that must be sufficiently fluid during pouring to distribute itself around the tubes in a desired manner exhibit only a limited temperature resistance that makes them unsuitable for the application of molten salts, for example, as a heat carrier.
Finally, it is known from the U.S. Pat. No. 4,127,389, to design the gas inlet and gas outlet hoods together with the associated tube plates as individual chambers within the reactor housing where said chambers are essentially surrounded on all sides by stream-calmed heat carriers. For this purpose, an unsealed plate penetrated by the contact tubes is located at a distance and parallel to each tube plate, where the one on the gas inlet side carries an insulation layer made of cast refractory material. This is a relatively narrow endothermic high-temperature reactor, whose heat carrier may exhibit a temperature of between 1075 and 870 1° C. and is, therefore, definitely in a gaseous state. Furthermore, the pressure difference between process gas and the heat carrier may be just about 7 bar at the most. Accordingly, the tube plates together with their suspensions can be made relatively light in weight. If they had to carry the liquid heat carrier in addition to the weight of the tubes, then the usual immediate anchoring at the reactor jacket would be unavoidable. This applies particularly for reactor designs with a comparatively great diameter and many tubes.